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520,173. Colour photography, SCHINZEL, K., and SCHINZEL, L. June 27, 1938, No. 31061/39. Convention date, June 25, 1937. Divided out of 516,536. [Class 98 (ii)] A three-colour photograph is produced in an exposed element having on a single support three differentially colour-sensitized silver chloride or chlorobromide emulsions each containing a leuco dye or derivative thereof by development of the latent images, conversion of the residual silver halide by double decomposition into a compound or compounds capable of oxidizing or catalysing the oxidation of the.leuco compounds, oxidation of the leuco compounds in the vicinity of the residual silver halide to give positive dye images, and removal of the developed silver. The element may have three superimposed silver chloride or chlorobromide emulsion layers for recording the picture images and a fourth silver bromide emulsion layer for recording the sound record, which may also be recorded in addition in one or more of the silver chloride or chlorobromide emulsion layers. The first development may be effected with quinine sulphonic acid and sodium sulphite, the residual silver chloride converted into silver ferrocyanide, and the latter converted into oxidizing compounds or compounds catalysing the oxidation of the leuco compounds such as lead or silver chromate, lead peroxide or manganese dioxide or vanadyl ferrocyanide by a neutral or weak alkaline bath, containing, for example, sodium carbonate or trisodiumphosphate. The sound record in the silver bromide layer .is developed, and the leuco dyes in the silver chloride layers are oxidised by treatment with inorganic acids, or, in the case of vanadyl ferrocyanide, sodium chlorate. The action is stopped and the silver removed by treatment with Farmer's reducer. The unused leuco compounds are removed by treatment with sodium hydroxide, if necessary with the addition of alcohol. The leuco sulphuric acid esters of vat dyes may be used, in particular the insoluble salts with di-and tri-phenylguanidine, quinine, aristochin, dicinchonine, auramine, and thioflavine. Other derivatives of leuco vat dyes and of generators of vat dyes and reduced anthraquinone dyes, their condensation products with aldehydes, and their carboxylic and sulphonic acids may also be used. The use of leuco bases of di-and tri-phenylmethane dyes, and precipitants such as phosphotungstates is referred to. Coloured leuco compounds may be used. A yellow leuco compound may be added to the top layer, or yellow or orange leuco compound to the middle layer, and a red leuco compound to the bottom layer. Wetting agents may be added to the emulsions to prevent coagulation. Aqueous solutions of indigosols may be poured into a silver halide gelatine emulsion containing dissolved precipitants and the leuco compound adsorbed on to the surface of the silver halide grains by vigorous agitation. The leuco compounds may be precipitated in the emulsion from acetone or alcohol solution and the emulsion washed and ripened. The process may be repeated several times by alternately adding precipitant and leuco compound. Precipitants for the leuco bases or colour sensitizers may be added to any intermediate layers. , An antihalation layer is provided. Specifications 379,679, 512,559 and 516,536 are referred to.
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